شواهد الکتروانسفالوگرافیک بازنمایی عصب شناختی مشخصه های آوایی ,و واجی واکه های زبان فارسی در قشر شنوایی مغز

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری زبان شناسی همگانی، دانشگاه تهران، تهران، ایران.

2 استاد گروه زبان شناسی همگانی، دانشگاه تهران، تهران، ایران

چکیده

پژوهش حاضر به بررسی رابطه بین مشخصه­ های آوایی و واجی واکه­ های ساده زبان فارسی و واقعه­ های
عصب­ شناختی متناظر با آن در دستگاه شناختی بشر می­ پردازد. بدین منظور با طراحی آزمایشی تجربی، از 20 نفر از گویشوران زبان فارسی خواسته شد تا به توالی­ هایی از واکه­ های ساده زبان فارسی با ترتیب تصادفی گوش کنند و همزمان پاسخ دستگاه عصبی آنان به شنیدن این واکه­ ها با استفاده از روش الکتروانسفالوگرافی ثبت شد. سپس با استخراج پتانسیل­ های وابسته به رخداد متناظر با پردازش هر واکه در قشر شنوایی اولیه مغز آنان، ویژگی­ ها و مشخصات این واکنش­ ها و نسبت آنان از یک سو با برجستگی­ های پنجره طیفی سیگنال صوتی (F1, F2 و F2-F1) و از سوی دیگر با مشخصه­ های ممیز واجی محل تولید و ارتفاع زبان بررسی شد. در این بررسی­ها مشخص شد قرار گرفتن در معرض هر یک از محرک­ های مورد استفاده در این آزمایش دستکم در دو مرحله پاسخ عصبی برجسته ­ای تولید می­کند که هر دو، هم با مشخصات طیفی­-زمانی محرک و هم با مشخصه­ های انتزاعی-مقوله­ ای واکه­ ها همبستگی آماری دارند. نتایج این پژوهش تاییدی بر این فرضیه است که فرآیند تفکیک ادراکی واکه ­ها از یکدیگر حاصل روندی تدریجی از نشان­گذاری بر اساس برجستگی­ های صوت­ شناختی تا مقوله­ بندی مشخصات واجی است که در مرحله اول در دو نیمکره مغز به صورت متقارن انجام می­شود و با برجستگی­ های صوت­ شناختی نسبت به مشخصه­ های واجی همبستگی بالاتری دارد، اما در مرحله دوم بار اصلی پردازش به نیمکره چپ منتقل شده و ویژگی­ های پاسخ عصبی به هر واکه در این مرحله مطابقت بالاتری با مشخصه­ های واجی نشان می­دهند. بدین­ ترتیب برجسته­ ترین ماحصل این پژوهش دست­یابی به نقشه «زمان­ نواختی» پردازش عصبی واکه­ های زبان فارسی و حوزه ادراکی مشخصه محل تولید واکه در دستگاه شنوایی گویشوران این زبان است. هرچند توان تفکیک اندازه­ گیری انجام شده در این آزمایش برای بیرون آوردن همبسته عصبی پردازش مشخصه ارتفاع زبان از زیر سایه اثر بزرگ­ تر مشخصه محل تولید کافی به نظر نمی­ رسد.

کلیدواژه‌ها


عنوان مقاله [English]

Electrophysiological Evidence of Neurological Representations of the Phonological and Phonetic Properties of Persian Vowels in the Auditory Cortex

نویسندگان [English]

  • Abbas Nasri 1
  • Gholamhosain Karimi doustan 2
1 Ph. D Candidate of Linguistics, University of Tehran, Tehran, Iran
2 Professor of Linguistics, University of Tehran, Tehran, Iran.
چکیده [English]

How the brain encodes the speech acoustic signal into phonological representations is a fundamental question for the neurobiology of language. The following paper is aimed to investigate the relationship between the phonological and phonetic properties of Persian simple vowels and neurophysiological events corresponding to them. To achieve such goal, we employed electroencephalography to map the Persian vowel system onto cortical sources using the N1 auditory evoked component. We found evidence that the N1 is characterized by asymmetrical indexes in the auditory areas of the cortex, structuring vowel representations. Properties of these ERPs were analyzed and modelled on one hand by the landmarks in the spectral window of their respective stimulus (such as F1, F2 and F2-F1) and on the other hand by the phonological distinctive features categorizing them (namely, height and place). The results revealed that the responses contain at least two distinguishable modulations of N1 components: a symmetric N1a which peaked between 113 to 149 milliseconds after the onset of the stimulus and a heavily left-leaning N1b which peaked between 149 to 170 milliseconds thereafter. Both N1a and N1b subcomponents showed strong correlations with a variety of parameters of both phonological and acoustic nature of the respective stimuli. However, N1a was significantly better modelled by acoustic factors while N1b displayed a better fit to a model based on phonetic factors. Based on such results, this paper argues that firstly the perceptual procedure of vowel categorization is a gradient process starting from demarcation of the stimulus signal according to acoustic landmarks which is done almost symmetrically then the processing load shifts significantly to the left hemisphere for the categorization of the input based on its perceived distinctive features. And secondly, that such information can be exploited to draft a ‘tonochronic’ map of such perceptual processes and define a perceptual field for every vowel and distinctive feature in the tonochronic space.

کلیدواژه‌ها [English]

  • auditory cortex
  • neurology of language
  • distinctive feature
  • Electroencephalography
  • perceptual representation
  • vowel system
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